Packet-oriented features like High-Speed Downlink Packet Access (HSDPA) and Enhanced Uplink (EUL) in a Universal Mobile Telecommunication System (UMTS) will promote the subscribers' desire for continuous connectivity. Continuous connectivity implies that users stay connected over a long time span, however with only occasional active periods of data transmission, in order to avoid frequent connection terminations and re-establishments causing inherent overheads and delays. This is the perceived mode that a subscriber is used to in fixed broadband networks (e.g. DSL) and a precondition to attract users from fixed broadband networks.
In order to support a high number of HSDPA users in the code limited downlink, a fractional DPCH (F-DPCH) has been introduced in release 6 of the 3GPP specifications. In the uplink on the other hand the limiting factor for supporting a similarly high number of E-DCH users is the noise rise. For high numbers of users in the cell it can be assumed that many users are not transmitting any user data for some time, e.g. for reading during web browsing or in between packets for periodic packet transmission such as VoIP. The corresponding overhead in the noise rise caused by maintained control channels will significantly limit the number of users that can be efficiently supported. As completely releasing of dedicated channels during periods of traffic inactivity would cause considerable delays for re-establishing data transmission and a corresponding bad user perception, the impact of control channels on uplink noise rise is to be reduced while maintaining the connections and allowing a much faster reactivation for temporarily inactive users. This is intended to significantly increase the number of packet data users, i.e. HS-DSCH/E-DCH users without UL DPDCH, in an UMTS FDD system that can stay in CELL_DCH state over a long time period without degrading the cell throughput and that can restart transmission after a period of inactivity with a much shorter delay (<50 ms) than would be necessary for re-establishment of a new connection.
The enhanced uplink concept, as illustrated in FIG. 2, implies the introduction of several channels from each user equipment for transmission in the uplink direction. The DPCCH carries pilot symbols and parts of the outband control signalling. Remaining outband control signalling for the enhanced uplink is carried on the E-DPCCH while the E-DPDCH carries the data transmitted using the enhanced uplink features. The HS-DPCCH carries the positive and negative acknowledgements (ACK/NACK) related to the HSDPA downlink transmissions and Channel Quality Indicators (CQI) to inform the Node B about the downlink channel conditions that are experienced by a particular user equipment. Similarly to the uplink in earlier releases of the WCDMA standard, the enhanced uplink uses inner and outer loop power control (OLPC). The power control mechanism ensures that a user equipment does not transmit with higher power than required for a successful delivery of the transmitted data (possibly using multiple transmission attempts). This ensures stable system operation and efficient radio resource utilization.
The document 3GPP TR 25.903 “Continuous Connectivity for Packet Data Users” issued by the 3rd Generation Partnership project (3GPP) discusses the following concepts:
SIR_target lowering: This proposed concept has the goal of substantially reducing the Tx power of the UL DPCCH, and thus the generated noise rise, by lowering the target parameter SIR_target for the signal-to-interference ratio (SIR) during idle traffic periods, i.e. when nothing needs to be transmitted in the uplink on the E-DPDCH. It is an important characteristic of this concept that these changes do not involve the radio network controller (RNC), so that the long delays of RRC or NBAP procedures (>>100 ms) are avoided and the user is staying in the CELL_DCH state. There are two different approaches how such a “SIR_target lowering” could be carried out: According to a first approach the serving Node B controls when a user equipment is going into an inactive phase with a lower SIR_target and a corresponding L1 signalling is used to trigger deactivation and reactivation. According to a second approach the user equipment controls, by help of a L2 MAC-e signalling, when the SIR_target in the Node Bs of the active RLS is lowered, i.e. deactivation and reactivation.
CQI off: This proposed concept has the goal to reduce the Tx power of the user equipment by stopping the reporting of Channel Quality Information (CQI), and thus eliminating the interference from HS-DPCCH in the uplink, when no data is transmitted on HS-PDSCH in downlink. Also here it is an important characteristic of this concept that these changes do not involve the radio network controller (RNC), so that the long delays of RRC or NBAP procedures (>>100 ms) are avoided and the user is staying in CELL_DCH state. There are two different approaches how the “CQI off” could be carried out: According to a first approach the serving Node B controls when a user equipment is going into an inactive phase with CQI off and a corresponding L1 signalling is used to trigger deactivation and reactivation. According to a second approach the user equipment controls CQI off by L2 MAC-e signalling to the Node Bs of the active RLS, i.e. deactivation and reactivation.
DPCCH gating: This concept follows the basic principle that, if there is neither E-DCH nor HS-DPCCH transmission, the user equipment automatically stops the continuous DPCCH transmission and applies a known DPCCH activity (DPCCH on/off) pattern. When an E-DCH or HS-DPCCH transmission takes place also the DPCCH is transmitted regardless of the activity pattern.
Other concepts consider that decisions about activity/inactivity are taken in the user equipment and communicated to the Node Bs using L2 signalling.